A New Approach to Fusion

A New Approach to Fusion

Power pistons: General Fusion’s reactor is a metal sphere with 220 pneumatic pistons designed to ram its surface simultaneously. The ramming creates an acoustic wave that travels through a lead-lithium liquid and eventually accelerates toward the center into a shock wave. The shock wave compresses a plasma target, called a spheromak, to trigger a fusion burst. The thermal energy is extracted with a heat exchanger and used to create steam for electricity generation. To produce power, the process would be repeated every second.

General Fusion, a startup in Vancouver, Canada, says it can build a prototype fusion power plant within the next decade and do it for less than a billion dollars. So far, it has raised $13.5 million from public and private investors to help kick-start its ambitious effort.

Unlike the $14 billion ITER project under way in France, General Fusion’s approach doesn’t rely on expensive superconducting magnets–called tokamaks–to contain the superheated plasma necessary to achieve and sustain a fusion reaction. Nor does the company require powerful lasers, such as those within the National Ignition Facility at Lawrence Livermore National Laboratory, to confine a plasma target and compress it to extreme temperatures until fusion occurs.

Instead, General Fusion says it can achieve “net gain”–that is, create a fusion reaction that gives off more energy than is needed to trigger it–using relatively low-tech, mechanical brute force and advanced digital control technologies that scientists could only dream of 30 years ago.

It may seem implausible, but some top U.S. fusion experts say General Fusion’s approach, which is a variation on what the industry calls magnetized target fusion, is scientifically sound and could actually work. It’s a long shot, they say, but well worth a try.

“I’m rooting for them,” says Ken Fowler, professor emeritus of nuclear engineering and plasma physics at the University of California, Berkeley, and a leading authority on fusion-reactor designs. He’s analyzed the approach and found no technical showstoppers. “Maybe these guys can do it. It’s really luck of the draw.”

The prototype reactor will be composed of a metal sphere about three meters in diameter containing a liquid mixture of lithium and lead. The liquid is spun to create a vortex inside the sphere that forms a vertical cavity in the middle. At this point, two donut-shaped plasma rings held together by self-generated magnetic fields, called spheromaks, are injected into the cavity from the top and bottom of the sphere and come together to create a target in the center. “Think about it as blowing smoke rings at each other,” says Doug Richardson, chief executive of General Fusion.

On the outside of the metal sphere are 220 pneumatically controlled pistons, each programmed to simultaneously ram the surface of the sphere at 100 meters a second. The force of the pistons sends an acoustic wave through the lead-lithium mixture, and that accelerates into a shock wave as it reaches the plasma, which is made of the hydrogen isotopes deuterium and tritium.

If everything works as planned, the plasma will compress instantly and the isotopes will fuse into helium, releasing a burst of energy-packed neutrons that are captured by the lead-lithium liquid. The rapid heat buildup in the liquid will be extracted through a heat exchanger, with half used to create steam that spins a turbine for power generation, and the rest used to recharge the pistons for the next “shot.”

The ultimate goal is to inject a new plasma target and fire the pistons every second, creating pulses of fusion reactions as part of a self-sustaining process. This contrasts with ITER, which aims to create a single fusion reaction that can sustain itself. “One of the big risks to the project is nobody has compressed spheromaks to fusion-relevant conditions before,” says Richardson. “There’s no reason why it won’t work, but nobody has ever proven it.”